Posted
by
Unknown Lameron Wednesday March 26, 2014 @10:47AM
from the neon-green-antineutrinos dept.

KentuckyFC (1144503) writes "The origin of the heat generated inside the Earth is one of the great mysteries of geophysics. Researchers know that almost all this heat is generated by the decay of radioactive elements such as potassium-40, thorium-232 and uranium-238. But what they don't know is how these elements are distributed inside the planet and how much heat each contributes. In the next few years, they hope to get some answers thanks to the emerging science of antineutrino geophysics. Since radioactive decay produces antineutrinos, an experiment that measures these particles coming out of the Earth should provide a detailed picture of the distribution of the elements within it.

But there's a problem. Nuclear reactors also produce copious numbers of antineutrinos and these can swamp the signal from inside the Earth. What's needed is a map showing the distribution of reactor antineutrinos so that geophysicists can choose the best places to put their experiments. Just such a map is exactly what a team of nuclear physicists has now produced. The map shows that planned experiments in Hawaii and Curacao, off the coast of Venezuela, are in excellent locations and that Japan has recently become a much better site thanks to the shut down of the country's nuclear industry following the 2011 Tohoku earthquake. But a European experiment currently being planned in south-east France doesn't come off so well."

When the Borexino experiment was being built (under the Appenines in Italy), they calculated that if a nuclear sub parked for more than a couple weeks in the same spot in the Adriatic, they'd be able to see it using neutrinos.

Not sure if anyone's redone that calculation now that the experiment works, but the preliminary one attracted some interest from the defense side of things.

There is a reasonably well thought out set of specs for "if DoD wants to use neutrino detectors to monitor nuke activity in, say North Korea, what would they have to build". Done from the perspective of the particle physics guys saying "if we can get DoD to spend some of its semi-infinite pile of cash on some neutrino detectors we're interested in, how would we do it?". The answer turns out to be almost feasible, actually. Here's only the most recent paper [arxiv.org] I bumped across, there are many others.

No. The map was made using existing data on known nuclear reactors and their power output and extrapolating what their antineutrino signature should look like. However, if geophysicists install detectors that show strong signatures that do not match up with the map given here, then that might be evidence for clandestine nuclear activity.

Yes. I see from the map that it's missing a number of known nuclear stations, for which the IAEA is unable to obtain data, and it's missing a number of "natural reactors" such as Oklu in Gabon, as well as a significant number of former Soviet reactors that are known to still be in use. It's also missing data for several Middle East reactors, known sites in South America, and a number of U.S. Military sites.

Assuming they get their experiment detectors running at all, they should be able to detect unreported nuclear reactor activity, but they'll have a hard time distinguishing it from the non-reactor related events they are seeking with the detectors.

In fact, radioactive heating was originally postulated as a source to make up for the inadequacies of frictional heating. But the magnitude of radioactive heating is orders of magnitude less than even frictional. As mathematicians would say, it may be "necessary, but not sufficient."

I'm not sure where you are getting your numbers from, but they don't seem to make any sense. Considering the heat released by the Earth is on the order of 40 TW, and frictional energy loss by the moon on the order of 3 TW (tidal heating from the sun much less) most of which is near the surface, this becomes a rather insignificant contribution to the heating of Earth.

You also keep claiming that the math just doesn't work for radioactive decay. If you assumed it was all from U-238, you would need about 4e18 kg of it to produce the required heating. If it was only located in the inner core, that amounts to only 40 ppm, which is a factor of 20 larger than the crustal abundance. If this was evenly spread out among the inner and outer core, you're talking about 2 ppm, which is not much higher than the crustal abundance.

There are a lot of questions about the specific details of the heat from which decay and exactly where in the Earth's structure. But that is wholly different than saying we have no idea and acting like the math is no where near the realm of possibility.